These files are inherently not plain-text, and to view them as such, you need a program which converts them from their format into text. Git is a program with components designed to do precisely that. I would be extremely surprised if anyone has written another one.
– CascabelOct 7 '09 at 15:38

If you want to view plain text form of git objects (commits and/or blobs i.e. file contents) without using git, it would not be easy, especially if repository is packed. Can't you install git locally, in your home directory (or its equivalent on MacOS X)?

The format for loose objects, stored as files in .git/objects/ fan-out directory, e.g. .git/objects/02/43019ddb4d94114e5a8580eec01baeea195133 (the fan-out directory and file name form SHA-1 identifier of object), is described e.g. in Chapter 9.2 "Git Objects" of "Pro Git" book (available on-line for free) and Chapter 7.1 "How Git Stores Objects" of "Git Community Book".

I'm going to interpret your question in a different way. If you want to understand what the objects files ARE, you can use git to view them directly, without navigating the history log or using git checkout, diff etc. For instance:

For the file .git/objects/04/a42e9a7282340ef0256eaa6d59254227b8b141

Run the command

git show 04a42e

which combines the 04 from /04/ and the first four characters of the remaining number a42e.

The index file contains a list of files with their metadata, including inode, permissions, and modification time. It also contains the SHA-1 of the content, which is stored as an object, which means that when you do git add it may create new objects.

I encourage you to create a simple test repo like git init init && cd init && echo a > a && git add a, and then hd .git/index to verify the format field by field.